Combustion control



. 26,1943'. 1 L KUNKER COMBUSTION CONTROL Filed sept. 15, 1941 JOHN- JT KLINKER atented Oct. 26, 1943 C USTN CONTROL John J. Klinker, Decatur, lill., assignor to A. W. Cash Company, Decatur, lll., a corporation of Delaware Application September 13, 194,1, Serial No. 410,788

4 Claims.

This invention relates to combustion control, and more particularly to the control of combustion in a furnace having a forced draft air supply which is started and stopped in accordance with the demand for heat. l

In furnaces of this type it is usual to start an stop the fuel supply at the same time as the air supply. The rate of fuel delivery during each operating period is ordinarily predetermined, but the rate of air flow usually Varies With the resistance of the fuel bed. If the fuel bed is slightly thin the air flow will be increased, thereby increasing the rate of combustion and causing the fuel bed to become even thinner. Consequently it is not possible to burn the fuel efliciently. This diiliculty becomes particularly serious when the demand for heat is low and the shut-down periods are prolonged, During such periods combustion continues at an appreciable rate because of air which passes through the forced draft fan by natural draft,` and the fuel bed therefore becomes badly depleted. Y

It is accordingly one object of the invention to provide a comparatively simple and eilicient apparatus for controlling combustion in a forced draft furnace of'the start and stop type.

It is a further object of the invention to provide a simple and dependable apparatus for main-I taining a predetermined rate of air flow in a forced draft furnace during the operating periods and for preventing substantially all air-now dur- Referring to the drawing illustrating one em' bodment of the invention, and in which like reference numerals indicate like parts, the single figure is a diagrammatic elevation, partly in section, of a forced draft furnace and associated combustion control apparatus.

The embodiment illustrated comprises walls III forming a furnace combustion chamber I I fired by means of an underfeed stokery I2 having al retort I and tuvre blocks I5. Air is supplied to the space I6 beneath the retort by means of a forced draft fan I8 driven by a motor I9. The motor illustrated is an electric motor directly connected to the fan, and it also serves to actuate the stoker t2 through a chain-and-sprocket drive 20. The heat from the furnace tl is utilized to generate steam `in a, boiler 22 mounted thereabove. The furnace gases flow in contact with the boiler heating surfaces and then escape through a gas outlet or uptake 23 to a suitable stack (not shown). The gas outlet 23 is provided with an adjustable damper 24 having an operating arm 25.

The damper 24 is controlled automatically by a suitable regulator responsive to variations in the pressure in the furnace II-. For this purpose I preferably utilize an automatic regulator 21 oi' the type disclosed in the patent to Temple No. 1,992,048 granted February 19, 1935. This regulator comprises a'pilot valve mechanism 28 supplied with a suitable uid under pressure through a pipe 29 and connected by tubes 3l to a hydraulic motor 32. This motor 32 is connected to the damper operating arm 25 by means of a rod 33. The regulator 21 is connected to the furnace Il by means of a pipe 34, so that the furnace pressurev is effective to 'actuate the regulator. The regulator is adjusted to maintain a furnace pressure slightly below atmospheric pressure, say a negative pressure of one-tenth inch water column. 'I'he electric motor I9 is connected to a suitable electrical supply 39 by means of conductors 31 which lead through an electro-magnetically `actuated switch 38. 'I'his switch is provided with a holding coil 39, and the parts are so arranged that upon energizati'on of this coil the switch will be closed and the motor I9 will start.

In order to control the rate of steam generation automatically, means is provided for start- I a predetermined minimum steam pressure and open at a predetermined maximum steam pressure. This switch 4I is connected in series with the coil 39 across two ofthe leads from the power supply 36, so that the master switch will control the operation of the switch 38. Obviously, a power source independent of the supply 36 could be utilized for control purposes if desired.

In order to control the rate of air flow to the furnace, a forced draft damper is shown mounted in the duct 46 between the fan I8 and the space I6 beneath the retort. This damperis provided with an operating arm 41 which is connected by a rod 49A to a hydraulic motor 50. This motor is controlled by a regulator 52 of the same type as the regulator 21 and comprising a pilot valve mechanism 53 supplied with a suitable luid under pressure through a pipe 54 and connected by a pair of conduits 55 to a fourway reversing valve 56, the latter being connected to the motor 50 by a pair-of conduits 51. The regulator 52 is subjected to a pressure differential which is a function of the rate of air flow to the furnace, and for this purpose I may utilize the pressure differential across the boiler gas passages. As shown. one side of the regulator is subjected to the pressure in the furnace Il through a pipe 58 connected to the pipe 34, and the other side of the regulator is subjected to the pressure in the gas outlet duct 23 anterior to the damper 24 through a pipe 59. With this construction, and the conduits 55 properly connected to the conduits 51, the regulator 52 will control the forced draft damper in such a way as to maintain a predetermined air ow to the furnace regardless of changes in the resistance of the Stoker fuel bed. x

The four-way'valve 56 is so constructed that the connections between the corl'duits 55 and 51 may be reversed when the stoker and fan are shut down, thus causlng-the motor to close the forced draft damper and stop substantially all air flow to the furnace. For this purpose the valve is provided with four aligned ports 6U, 6I, 62 and 63, and with a reciprocable valve member 65 having two aligned valve disks 66 and 61 thereon. The disk 66 is located between the ports 60 and 6|, whereas the disk 51 is located between the ports 62 and 63. 'I'he valve member 65 is actuated by a solenoid 68 which is connected across two of the conductors 31 between the stoker motor I9 and the switch 38. The arrangement is such that when the stoker is shut down the solenoid 58 will be deenergized, and the disks '55 and 61 will close the ports 6i and 63 as shown, the ports 60 and 62 being open. This will connect the conduits to the conduits 51 in such a way as to cause the moto'r 5U to close the forced draft damper 45. When the stoker is operating, the solenoid 68 will be energized, and the valve member will be raised to close the ports and 62, thus reversing the connections between the conduits 55 and 51, and causing the regulator 52 to control the forced draft damper 45 to maintain a predetermined rate of air flow.

The operation of the invention will now be apparent from the above disclosure. Assuming that the steam pressure is sufficiently high, the various parts will be positioned as illustrated. The master switch 4| will be open, the coil 39 will be deenergized, the switch 38 will be open, and the stoker motor i9 will be shut down. The regulator 21 will hold the damper 24 nearly closed, main taining a slight predetermined draft in the furnace Il. The solenoid 68 will be deenergized and the valve 56 will connect the conduits 55 and 51 in such a manner that the motor 50 will close the forced draft damper 45, the regulator 52 being subjected to a lower pressure differential than that for which it is adjusted. Thus the damper 45 will be closed during the shut down period so that substantially no air can enter the furnace Il. If now the steam pressure drops sufficiently to close the master switch 4|, the coil 39 will be energized, the switch 38 will close and the motor I9 will start the fan I8 and stoker I2. The solenoid 68 will be energized, reversing the valve 56 and causing the regulator 52 to control the forced draft damper in accordance with the pressure differential'across the gas passages of the boiler 22, as transmitted through the pipes 58 and 59. Since the regulators 21 and 52 are of the same typeftlie forced draft damper 45 will not open any faster than the uptake damper 24 will.

be opened-to accommodate the increasing gas flow, so that no objectionable flare-backs will occur during the starting of the fan. The forced draft damper 45 will be automatically controlled by the regulator 52 to provide a predermined rate of air iiow during each operating period, making it possible to maintain a desired fuel-air ratio despite changes in fuel bed resistance. As combustion continues and the steam pressure rises suiliciently to open the master switch 4I, the coil 39 will be deenergized, the 'switch 38 will open, the motor I8 will stop, and the parts will be restored to the positions shown` in the drawing until the start of the next operating cycle.

It will be understood that many changes and variations may be made in the construction and arrangement of the various parts without departing from the spirit of the invention, and therefore it is intended to include all such changes and variations within the scope of .the following claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A control system for a furnace having fuel supply means, a fan to supply forced draft air and a forced draft damper comprising means to start and stop the fuel supply means and the fan in accordance with the demand for heat a motor to actuate the damper, a regulator responsive to the rate of air flow and having a pilot mechanism, connecting means from the pilot mechanism to the motor so arranged that upon a decrease in the rate of air flow the motor will move the damper toward open position and vice versa, and means effective when theY fan is stopped to reverse the said connecting means so that upon a decrease in the rate of air flow the motor will move the damper toward closed position, thereby closing the damper when the fan is stopped.

2. A control system for a furnace having a passage for the flow of heating gases, fuel supply means, a fan to supply forced draft air and a forced draft damper comprising means to start and stop the fuel supply means and the fan in accordance With the demand for heat, a motor to actuate the damper, a regulator responsive to the pressure drop in the passage and having a .pilot mechanism, connecting means from the pilot mechanism to the motor so arranged that upon a decrease in the said pressure drop the motor will move the damper toward open position and vice versa, and means effective when the fan is stopped to reverse the said connecting means so that upon a decrease in the said pressure drop the motor will 'move the damper toward closed position, thereby closing the damper when the fan is stopped.

3. A control system for a furnace having fuel supply means, a fan to supply forced draft' air and a forced draft damper comprising means to start and stop the fuel supply means and the fan in accordance with the demand for heat, a hydraulic motor to actuate the damper, a regulator responsive to the rate of air flow and having a pilot valve, connecting means for the flow of pressure fluid between the pilot valve and the motor so arranged that upon a decrease in the rate of air flow the motor will move the damper toward open position and vice versa, the said connecting means including a reversing valve, and means effective when the fan is stopped to actuate the said reversing valve so that upon a assenso 3 decrease in the rate of air iiow the motor will move the damper toward closed position, thereby closing the damper when the fan is stopped.

4. A control system for a, furnace having fuel supply means, a fan to supply forced draft air 5 and a forced draft damper comprising means to` start and stop the fuel supply means and the fan in accordance with the demand for heat, a double-acting hydraulic motor to actuate the damper, a regulator responsive'to the rate of air iiow and having a pilot valve two conduits for the now of pressure uid in opposite directions i0 the fan is stopped.

JOHN J. KLINKER. 

